Current approaches to hcci worked

According to a paper I download and read (can't find the link now), it said that if none of the current approaches to hcci worked, there was a backup plan in which they would inject fuel or fire a spark to initiate combustion. The burning gases would compress the unburnt gases before the flame has time to travel forward and initiate autoignition. However this is not being pursued currently due to cost and complexity.

It was written that essentially, it would be a soft knock mode.

Are the benefits of the HCCI so high that even soft knocking is acceptable?

edit: Found the link: http://scholar.google.com/url?sa=U&q=http://www.llnl.gov/tid/lof/documents/pdf/234668.pdf [Broken]